Cross-cultural adaptation and psychometric testing of the Dutch and German versions of the Evaluation of Daily Activity Questionnaire in people with rheumatoid arthritis.

The Evaluation of Daily Activity Questionnaire (EDAQ) is a detailed patient-reported outcome measure of activity ability. The objective of this research was to assess the linguistic and cross-cultural validity and psychometric properties of the EDAQ in rheumatoid arthritis for Dutch and German speakers. The EDAQ was translated into Dutch and German using standard methods. A total of 415 participants (Dutch n = 252; German n = 163) completed two questionnaires about four weeks apart. The first included the EDAQ, Health Assessment Questionnaire (HAQ) and 36-item Short-Form v2 (SF-36v2) and the second, the EDAQ only. We examined construct validity using Rasch analysis for the two components (Self-Care and Mobility) of the Dutch and German EDAQ. Language invariance was also tested from the English version. We examined internal consistency, concurrent and discriminant validity and test-retest reliability in the 14 EDAQ domains. The Self-Care and Mobility components satisfied Rasch model requirements for fit, unidimensionality and invariance by language. Internal consistency for all 14 domains was mostly good to excellent (Cronbach's alpha ≥ 0.80). Concurrent validity was mostly strong: HAQ rs = 0.65-0.87; SF36v2 rs = - 0.61 to - 0.87. Test-retest reliability was excellent [ICC (2,1) = 0.77-0.97]. The EDAQ has good reliability and validity in both languages. The Dutch and German versions of the EDAQ can be used as a measure of daily activity in practice and research in the Netherlands and German- speaking countries.